学步园

//poj2365 好水啊  小学生都会吧 
#include <iostream>
#include <string>
#include <math.h>
#include <iomanip>
using namespace std;
int main()
{
	int n;
	double r;
	cin>>n;
	cin>>r;
	double x[105], y[105];
	double length = 0;
	for(int i = 0; i < n; i++)
	{
		cin>>x[i]>>y[i];
		if(i != 0 )
			length += sqrt(pow((x[i] - x[i-1]), 2) + pow((y[i] - y[i-1]), 2));
		if(i == n-1)
			length += sqrt(pow((x[n-1] - x[0]), 2) + pow((y[n-1] - y[0]), 2));		
	} 
	length += 2 * 3.1415926 * r;
	cout<<fixed<<setprecision(2)<<length<<endl;
	return 0;
}